Yes - over time supplies tend to change due to demand, of course, but that's 'long run' stuff ... not in that chart. The author is kind of misinterpreting the chart.
2) It's not 'sunk cost' that's the issue, this is about 'fixed' vs. 'unit' cost. Software is all 'fixed' (i.e. setting up the production line) whereas most material things are mostly about 'unit' costs (i.e. the cost to make an item)
3) Software sales are a tiny fraction of the economy because almost nobody is selling software. People are selling 'services', basically products that 'do stuff using software'.
The 'key ingredient' is usually some type of business or experiential knowledge, not some algorithm.
4) Software development doesn't finish at v1, it's ongoing.